Javascript/JQuery - val().length' 为 null 或不是对象
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Javascript/JQuery - val().length' is null or not an object
提问by user532104
I have the error val().lengthis null or not an object" from code:
我有错误val().length为空或不是对象”来自代码：
function size(sender, args) {
var sizeVariable = $("input[id$='txtHello']");
if (sizeVariable.val().length == 0)
{
args.IsValid = false;
}
}
The error occurs on the "If" statement. I am trying to check if:
错误发生在“If”语句上。我想检查是否：
- the variable exists
- if there is something in the variable
- 变量存在
- 如果变量中有东西
I think the problem lies with point (1). How do I check if the text field exists (to hopefully resolve the issue)?
我认为问题在于点（1）。如何检查文本字段是否存在（希望能解决问题）？
回答by dxh
You can test if the input field exists as such:
您可以测试输入字段是否存在：
if($("input[id$='txtHello']").length > 0) { ... }
If it doesn't, val()will return undefined.
如果没有，val()将返回undefined。
You could skip immediately to the following:
您可以立即跳到以下内容：
if(!!$("input[id$='txtHello']").val())
... since both undefinedand ""would resolve to false
......因为这两个undefined和""将解析false
回答by Steve Jalim
Try if (sizeVariable.val() == undefined || sizeVariable.val().length == 0)instead. That way, it'll check whether there's a value first, before trying to see how long it is, if it is present
试试吧if (sizeVariable.val() == undefined || sizeVariable.val().length == 0)。这样，它会先检查是否有一个值，然后再尝试查看它有多长，如果它存在
回答by BvdVen
make your check like this
像这样做你的支票
if (sizeVariable.val() === undefined || sizeVariable.val().length == 0)
回答by WraithNath
is sizeVarialbe null when trying to check the length?
尝试检查长度时 sizeVarialbe 是否为空？
function size(sender, args) {
var sizeVariable = $("input[id$='txtHello']");
if (sizeVariable != null)
{
if (sizeVariable.val().length == 0)
{
args.IsValid = false;
}
}
else
{
alert('error');
}
}
回答by baked
Have you tried...?
你有没有尝试过...？
if( sizeVariable.size() == 0 )
{
args.IsValid = false;
}
回答by Yousif Al-Raheem
In jQuery you can use:
在 jQuery 中，您可以使用：
if( input.val().length > limit)
or if for some reason it didn't work you can use:
或者如果由于某种原因它不起作用，您可以使用：
if( ( input.val() ).length > limit )
